Generally, a gas turbine includes a compressor, a combustor, and a turbine, and is configured to combust air compressed by the compressor and fuel in the combustor to produce combustion gas having a high temperature and a high pressure, and to drive a turbine with the combustion gas to obtain power. A turbine includes blade rows disposed inside a casing, the blade rows including a plurality of turbine stator vanes and a plurality of turbine rotor blades arranged alternately. Combustion gas is taken into the casing to drive the turbine rotor blades to rotate, thereby rotating a rotor coupled to the turbine rotor blades.
In such a turbine, normally, clearance is provided between the casing and tip ends of the turbine rotor blades so as not to cause rubbing due to a difference in thermal expansion between the casing and the turbine rotor blades.
However, during operation of a gas turbine, a part of a main flow of combustion gas may leak out through the clearance from a pressure side to a suction side of turbine rotor blades without performing work, due to a pressure difference between the pressure side and the suction side. Besides failing to perform work on the blade rows of the turbine, a leakage flow through the clearance rolls up at the outlet side of the clearance to form a longitudinal vortex, and mixes with the main flow, which may lead to generation of pressure loss. Loss due to a leakage flow through the clearance is one of the main factors that deteriorate the turbine efficiency.
In this context, to reduce loss due to a leakage flow through the clearance, known is a configuration provided with a squealer rib formed on a tip end of a turbine rotor blade, as disclosed in U.S. Pat. No. 8,684,691B and JP2011-163123A. A squealer rib is a fence-shaped projection formed along an outer periphery of a tip surface of a turbine rotor blade, also called as a squealer. With a squealer rib provided on a tip end of a turbine rotor blade, a flow-path resistance in the clearance increases, and the contraction-flow effect reduces the amount of leakage flow through the clearance. U.S. Pat. No. 8,684,691B and JP2011-163123A also disclose a squealer rib with an inclined side face.